Method to obtain a refractory composite material based on carbide

ABSTRACT

A method to obtain a refractory carbide-based composite material, in particular as an article of a predetermined shape includes the following steps: molding of a porous blank from a mixture of powders of at least one carbide-forming metal and/or non-metal and at least one carbide, the amount of carbide component in the mixture of powders not exceeding 90%, heat treating the obtained porous blank in a hydrocarbonous atmosphere containing one or more hydrocarbons until the increase in its mass reaches 2-42%, thereby obtaining a semi-product, and heating the obtained semi-product in a non-oxidizing medium at a temperature of 1000-2000° C.

CROSS REFERENCE TO RELATED APPLICATION

This is the 35 USC 371 national stage of International ApplicationPCT/EP00/11025 filed on 8 Nov. 2000, which designated the United Statesof America.

FIELD OF TECHNOLOGY

The present invention relates to the field of manufacturing acarbide-based refractory composite material and more particularly, tothe method to manufacture a refractory composite article withpredetermined shape and dimensions.

BACKGROUND OF THE INVENTION

A known method for obtaining a refractory composite article based on atleast one refractory compound, includes the following stages (U.S. Pat.No. 3,725,015):

-   -   Mixing of powder refractory material, boride and/or carbide,        with a carbon-containing substance.    -   Molding of a blank in a predetermined shape out of the mixture.    -   Heating of the obtained blank for extraction of carbon out of        the carbon-containing substance.    -   Impregnation of the blank with a molten metal alloy comprising        75-99% vol. of at least one metal out of the group containing        Si, Cr, Fe, Ni, Ti and 1-25% vol. of a metal or mixture of        metals out of the group Al, Cu, Fe and 0-24% vol. of a metal        contained in the initial refractory material.

This known method has a number of drawbacks. For instance, the use oforganic substances as the source of carbon demands a high processtemperature at the decomposition stage. Such decomposition occurs in thevolume of the molded blank with release of great amount (up to 50% ofbond mass) gaseous substances. It often causes defects (cracks) in theblank. Further more the use of reaction-active alloys at theimpregnation means that, during the impregnation the alloy componentsinteract with carbon and form solid carbides. The solid carbides blockpores, thus impeding further impregnation as well as the formation of apore less material with a uniform structure.

Another known method for obtaining a refractory composite material inthe form of an article with predetermined shape is disclosed in Patentapplication PCT/EP97/01566 According to this method a porous blank,having a porosity of 20-60% vol., is being molded from a powder made outof a carbide-forming metal. Then the blank is being heat treated inatmosphere of gaseous hydrocarbon or hydrocarbon mixture at atemperature exceeding the temperature of their thermal decompositionuntil the weight of the blank has increased at least 3%. Next thesemi-product is being impregnated with melt of a metal out of the groupincluding the following metals: Ag, Au, Cu, Ga, Ti, Ni, Fe, Co or analloy based on a metal out of this group.

As carbide-forming metal, a metal out of group IV, V or VI of thePeriodic table is used, e.g. Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W. Heattreating is carried out in a hydrocarbonous atmosphere containing one ormore hydrocarbons out of the group that comprises acetylene, methane,ethane, propane, pentane, hexane, benzene and their derivatives. Ashydrocarbon mixture for heat treatment natural gas can be used. Thescope of good properties allows the use of materials manufactured bythis known method as refractory structural materials, erosion-resistantelectrodes of plasmotrones, erosion-resistant heavy-current electriccontacts, arc-suppressing elements, high-temperature heat accumulators,ablating heat-shielding materials and heat-resistant damping materials.As a rule, materials produced by this known method have a high specificdensity, which restricts the field of their application. Whenmanufacturing an article according to this method, great care has to begiven to the process parameters during the pyrocarbonization- andactivation-heat treatments so that a distortion of the intermediatebody, in form of warpage does not occur. The distortion that can occuris caused by the transformation of the carbide-forming agent to carbide,e.g. when Ti transforms to TiC.

SUMMARY OF THE INVENTION

It is an object of the present invention to develop a method assuringthe production of a refractory composite material possessing as good orbetter characteristics as those of materials manufactured by the knownmethods but by a simpler, more controllable and less energy consumingprocess than the known methods. Molding of blank out of a powder mixtureof carbide-forming metals and/or non-metals and their carbides (incontrast to the known concepts) offers a number of advantages First ofall, the use of both carbides and metal and/or non-metal in the powdermakes it easier to achieve a favorable size distribution of the powderparticles in order to optimize the packing properties of the powder. Itprovides the possibility to optimize the composition and porosity of theblank even in case of restricted choice of carbide and metal and/ornon-metal powders on the market. Secondly the use of mixtures of carbideand metal/non-metal carbide formers leads to a substantially decrease inthe duration of the pyrocarbon heat treatment in comparison with priorart. Thirdly in contrast to prior art, the use of both carbide andcarbide forming agent in the mixture makes it easier to keep the porousbody and semi product free of any distortion occurring during thepyrocarbon- and activation-heat treatments, i.e. with less effort put oncontrolling the process it is possible to manufacture a high-qualityarticle. It is also an object of the present invention to develop amethod assuring the production of a refractory composite articlepossessing high physical and mechanical characteristics combined withlow specific density. Such an article will also posses high hardness andgood wear resistance, high thermal and electric conductivity and be ableto work at elevated temperatures. The developed method will also givethe possibility to change the listed properties by varying theproportion of the components and by varying the manufacturing parametersthus, obtaining articles having a wide field of properties andapplications.

The present invention can be divided into the following steps

-   -   Molding of a porous blank having a porosity of 20-70%. The blank        consisting of a powder mixture, containing at least one        refractory carbide-forming metal and/or refractory        carbide-forming non-metal and at least one carbide. The content        of carbide in the powder mixture forming the blank does not        exceed 90W %. The blank can contain an added temporary binder.    -   Heat treatment of the porous blank in an atmosphere of gaseous        hydrocarbon or hydrocarbon mixture at a temperature exceeding        the temperature of their thermal decomposition until the blank        has increased 2-42/mass.    -   Heating of the obtained semi-product in a non-oxidizing medium        at a temperature of 1000-2000° C.    -   Impregnation of the obtained semi-product by a melt of metal or        alloy.

In the first embodiment of the claimed invention the porous blank isformed of a powder mixture consisting of at least one of the refractorycarbide-forming elements in the group, Ti, Zr, Hf, V, Nb, Ta, Mo, Cr andW, and at least one carbide of the elements of said group. The porousblank has porosity in the range of 20-60%. Heat treatment in anatmosphere of gaseous hydrocarbon mixture is carried out until the blankincreased 2-25% in mass. The obtained semi-product is heated in anon-oxidizing gas atmosphere (e.g. in vacuum or inert gas) at 1000-2000°C. and then impregnated with a melt either consisting of at least oneelement in the group; Si, Mg, Al, Ag, Au, Cu, Ga, Ti, Ni, Fe, Co or ofan alloy based on at least one element of said group.

Another Embodiment of the claimed invention stresses the low-densityproperties as well as the possibility to use two different carbideformers. The porous blank, having a porosity of 30-70% vol., is formedof a mixture consisting of boron and/or silicon, and boron carbideand/or silicon carbide. The blank is subjected to heat treatment in anatmosphere of gaseous hydrocarbon or a mixture of hydrocarbons at atemperature exceeding the temperature of thermal decomposition of saidhydrocarbon or hydrocarbon mixture until the blank has increased 8-42%in mass, then the semi-product is heated at 1300-1800° C. in an inertmedium and impregnated with a melt of a element in the group; Si, Al, Mgand Cu or of an alloy based on at least one element of said group.

In all said embodiments forming of the blank can be carried out by anyknown method feasible in this case to obtain an article with necessaryporosity, e.g. by pressing, slurry or tape casting.

In all said embodiments the blank can be formed in such a way that thepores are uniformly or non-uniformly (gradient) distributed through thevolume of the blank. When forming a blank with uniform distribution ofporosity, the impregnating metal, alloy or Si phase is distributeduniformly in the composite material. In the case of non-uniformdistribution of porosity in the blank the distribution of theimpregnating metal, alloy or Si phase will be non-uniform as well.

In all said embodiments the blanks are heat treated in an atmosphere ofa gaseous hydrocarbon or hydrocarbon mixtures at a temperature exceedingtheir thermal decomposition temperature. When using a hydrocarbon orhydrocarbon mixture out of the group: acetylene, methane, ethane,propane, pentane, hexane, benzene and derivatives of the listedcompounds the temperature is held in the range of 550-1200° C. Whenusing natural gas as the hydrocarbon mixture optimum temperature rangeis 750-950° C.

In all said embodiments the impregnation is carried out in an inertatmosphere by dipping the semi-product into the melt or by melting anamount of metal alloy or Si on its surface.

DETAILED DESCRIPTION OF THE INVENTION

The method according to the present invention includes the followingsteps:

-   -   Forming of the porous blank with a porosity of 20-70% of a        powder mixture containing at least one refractory        carbide-forming agent, and at least one carbide. Content of        carbide powder in the mixture does not exceed 90 W %.    -   Heat treatment of the porous blank in an atmosphere of gaseous        hydrocarbon or hydrocarbon mixture at a temperature exceeding        the temperature of their thermal decomposition until the mass of        the blank has increased by 2-42%.    -   Heating of the obtained semi-product in a non-oxidizing medium        at a temperature between 1000-2000° C.    -   Impregnation of the obtained semi-product with a melt consisting        of one metal alloy or Si.

The porous blank is formed by using known forming methods, e.g.pressing, slurry casting or tape casting. The preferred range ofporosity in the blank is 20-70% vol. the blank can be molded with auniform distribution of pores through its volume or with a non-uniform(gradient) distribution of pores through its volume. When forming ablank with uniform distribution of porosity, the impregnating metal,alloy or Si phase is distributed uniformly in the composite material. Inthe case of non-uniform distribution of porosity in the blank thedistribution of the impregnating metal alloy or Si phase will benon-uniform as well. The obtained porous blank is heated in anatmosphere of a gaseous hydrocarbon or hydrocarbon mixture at atemperature exceeding the temperature of decomposition of thehydrocarbon or hydrocarbon mixture. When using a hydrocarbon orhydrocarbon mixture out of the group acetylene, methane, ethane,propane, pentane, hexane, benzene and derivatives of the said compoundsthe temperature is held in the range of 550-1200° C. When using naturalgas the optimum temperature range is 750-950° C. The heat treatment iscarried out until the mass of the blank has increased by 2-42% Theobtained semi-product is heated in a non-oxidizing gas atmosphere (e.g.in vacuum or inert gas) at 1000-2000° C. and then impregnated with amelt either consisting of at least one element in the group; Si, Mg, Al,Ag, Au, Cu, Ga, Tic Ni, Fe, Co or of an alloy based on at least oneelement of said group

The manufacturing parameters depend upon the environment where therefractory composite material is to be placed as well as on what type offunction the article is going to fulfill. Consequently the manufacturingparameters are varied from case to case. The properties of the articlecan be varied by choice of:

-   -   The composition of the powder mixture used for molding of the        blank;    -   The hydrocarbon or mixture of hydrocarbon used at the stage of        heat treatment;    -   The substance used for impregnation.

The particle size distribution of the initial metal and/or non-metal andcarbide powders are chosen according to the desired porosity formationin the blank (volumetric content and the size of the pores).

Description Step By Step

The porous blank is formed by using known forming methods, e.g.pressing, slurry casting or tape casting. The use of carbides and metaland/or non-metal in the powder makes it easier to achieve a favorablesize distribution of the powder particles in order to optimize thepacking properties of the powder. It provides the possibility tooptimize the composition and porosity of the blank even in case ofrestricted choice of carbide and metal and/or non-metal powders on themarket. The preferred range of porosity in the blank is 20-70% vol. Atporosity below 20% the processes of molding, heat treatment andimpregnation are impeded. The fact that the impregnation is impededmeans that the content of metal or Si phase in the obtained compositematerial is small, thus the advantages of this type of materialconnected with presence of metal phase cannot be realized in fullmeasure. Porosity above 70% is not advisable because reduced content ofcarbide skeleton in the composite material deteriorates the propertiesof the composite material.

For articles such as filters and catalyst substrates that have lowerdemands on the mechanical strength or lower demands on the metal phase,porosities outside the above mentioned range can be used. However, askeleton carbide body having a lower porosity than 8% or a higherporosity than 75 will have a too poor performance to be useful.

Use of powder mixtures with a carbide content of more than 90 W % is notadvisable since it leads to a physically weak semi-product. The amountof carbon being deposited is determined by the amount of availablenon-carbide precursor to react with. Consequently a to high percentageof carbide in the powder mixture leads to the semi-product not havingenough strength to endure the following steps in the manufacturingprocess.

The blank can be molded with a uniform distribution of pores through itsvolume or with a non-uniform (gradient) distribution of pores throughits volume. When forming a blank with uniform distribution of porosity,the impregnating metal phase is distributed uniformly in the compositematerial. In the case of non-uniform distribution of porosity in theblank the distribution of the impregnating metal phase will benon-uniform as well.

The proportions between the components when mixing the powder areexemplified below for Ti and Si/B:

When using Ti and TiC the proportions varies as follows, numbers givenin mass %: Titanium 30-99 and Titanium carbide 1-70.

When using Ti, TiC and a temporary binder the proportions varies asfollows, numbers given in mass %: Titanium 29-98, Titanium carbide 1-69and Temporary binder 1-5.

When using Si and/or B and SiC and/or B₄C the proportions varies asfollows, numbers given in mass %: Boron or silicon or a mixture of them30-99 and Boron carbide or Silicon carbide or a mixture of them 1-70

When using Si and/or B and SiC and/or B₄C and a temporary binder theproportions varies as follows, numbers given in mass %: Boron or siliconor a mixture of them 30-98, Boron carbide or Silicon carbide or amixture of them 1-70 and Temporary binder 1-5.

The porous blank manufactured from the powder mixture is thentransformed into a carbide skeleton by means of a chemical synthesis ofcarbide carried out in the volume of the blank. For this purposesynthesis of pyrocarbon is firstly carried out in pores of the blank.Pyrocarbon is formed in the volume of the blank according to thefollowing chemical reaction:C_(m)H_(n)=mC+n/2H₂  (3)

Therefore the process is carried out under conditions when reaction (3)is displaced to the right, i.e. at temperatures exceeding decompositiontemperature of the hydrocarbon in question. In order to provide uniformpyrocarbon formation in all the pores of the blank a balance must bekept between the decomposition rate and the diffusion coefficients inthe pores. Such a balance is achieved by determining the optimumtemperature for each combination of porous body and pyrocarbon source.When using hydrocarbons out of the group: acetylene, methane, ethane,propane, pentane, hexane, benzene and their derivatives it is advisableto choose a temperature in the range of 550-1200° C., when using naturalgas optimum temperature lies in the range of 750-950° C. During thepyrocarbon part of the heat treatment an increase in mass of the blanktakes place, this increase is determined by the deposition conditionsand the duration of the heat treatment.

The desired mass increase of the blank is in each specific casecalculated from the stoichiometric proportion between metal/non metaland carbon in the carbide (M_(m)C_(n)) that is to be formed, using thefollowing dependence:Δm=m₀·α·(M_(c)·v/M)·K  (1)

Where:

-   -   Δm—mass change of the blank;    -   m₀—initial mass of the blank;    -   α—amass portion of metal/non-metal in the mixture;    -   M_(c), M—mole masses of carbon and metal/non-metal forming the        carbide;    -   v—correlation of stoichiometric coefficients v=n/m in chemical        formula of carbide M_(m) C_(n);    -   K— non-stoichiometricity coefficient, 0.5≦K≦1.

Equation 1 is used when using powders of one carbide-formingmetal/non-metal as well as when using several carbide-formingmetals/non-metals. In the later case the calculation is carried outapplying equation (1) for each one of the metals/non-metals.

When using a mixture containing a temporary binder it is more convenientto use another dependence:Δm=m₀·[1/(1+β)](M_(c)·v/M)·K  (2)

Where β is the ratio between mass of carbide and mass of metal/non-metalin the mixture.

The increasing mass of the porous body will change the shape of thisbody in a micro-scale perspective, the porosity thereof being reduced.However, in a macro-scale perspective the shape and size of the porousbody formed at the molding will not undergo any noticeable change. Thesemi-product obtained after the pyrocarbon process has thus inmacro-scale perspective the same shape and size as the porous bodyobtained in the molding process.

The Preferable range of blank mass change in the atmosphere ofhydrocarbons is 2-42%. At blank mass changes less than 2% a substantialdeformation of the semi-product takes place at the following stage(heating in non-oxidizing medium). The material has not enough carbonacting as a binding agent to be able to withstand the high stressesexperienced at the heat treatment. A blank mass change by more than 42%results in an excess of carbon that has been deposited during thepyrocarbon process, which is not being synthesized into carbide. Thisexcess of free carbon reduces the wetability between pores and metal atthe impregnation step, which in the end, results in the deterioration ofthe properties of the final composite material.

The use of mixtures of carbide and metal/non-metal carbide formers leadsto a substantial decrease in the duration of the pyrocarbon heattreatment in comparison with prior art. This decrease is connected withthe fact that these mixtures of precursor substances are fastertransformed into the required composition during the heat treatment thanmixtures consisting of only metal/non-metal carbide formers are. Thedecrease in needed time for the heat treatment can be understood by ananalysis of equation (1). When using carbide—metal mixtures the value ofa becomes less than 1, α decreases with increase in mass share ofcarbide in the mixture. It can be seen from equation (1) that Δmdecreases when α decreases. As a result of a decreased change in theblank mass, the duration of the heat treatment becomes shorter. As anexample, the period of heat treatment for a blank formed from titaniumpowder is 23 hours. This period is sufficient to reach thestoichiometric Ti:C ratio. While the period of heat treatment for ablank consisting of 50% Ti and 50% TiC is 11 hours, at the sameconditions (see Examples no. 3, 4). When decreasing the duration of theprocess also the amount of energy and reagents consumed by the processare being decreased. Thus the cost of the process is reduced.

When the pyrocarbon synthesis has been completed the semi-productrepresents a chemically meta-stable system consisting of partlycarbide-forming metal and/or non-metal and partly deposited carbon,these two constituents are able to react and form carbides. The reactionis activated by temperature. Therefore, the semi-product is heated in anon-oxidizing atmosphere (e.g. in vacuum or argon) to a temperaturebetween 1000-2000° C. for a time sufficient for formation of secondarycarbide. As a rule, this time is at least 15 min and depends oncomposition and size of the semi-product. The carbide is beingsynthesized by the reaction between metal and/or non-metal and carbonresulting in a body consisting completely of carbide, the body having athree-dimensional skeleton structure. The degree of porosity in thecarbide skeleton obtained by this method being 15-60% vol. andpractically all pores have an open structure.

When the intention is to use the material/article as a filter, thematerial/article is now ready for use.

In contrast to prior art the use of carbide-metal/non-metal mixturesprevents or significantly decreases the risk of a deformation of theporous body and semi product during the pyrocarbon- and activation-heattreatments. The use of carbide particles in the powder prevents orsignificantly decreases the strain that can be built up in the materialwhen the carbide-forming element is being transformed to carbide. Thisstrain has its origin in the shape and size difference between thecrystal-structure of the carbide-former and the crystal-structure of thecarbide, e.g. the transformation of Ti to TiC cause deformation of thebody during the transformation process of the metal/non-metal particlesinto carbide. A body less prone to shape changes during themanufacturing make it possible to simplify the control of the heatingprocesses. It makes it possible to accelerate the process at the step ofheating as well as decrease the requirements on the temperaturecontrolling equipment. Hence the method becomes easier to manage,shorter in time and requiring less expensive equipment.

Impregnation of the carbide skeleton body by the metal, alloy or Si meltis carried out in a non-oxidizing atmosphere (e.g. vacuum or argon) bydipping the carbide skeleton body into a melt or by melting of a amountof metal, alloy or Si on the surface of the carbide skeleton body.Capillary forces fill the pores of the carbide skeleton body until allthe pores are completely filled by the melt. The temperature at thestage of impregnation depend on the melting point of the metal alloy orSi, e.g. for Cu the temperature is held between 1300-1350° C., for aCu—Ga alloy (4:1) the temperature is held between 1000-1050° C., for aTi—Ni alloy the temperature is held between 1250-1300° C. and so on. Thepreferred content of metal or Si phase after the impregnation process is15-60% vol. When the metal, alloy or Si has so-lidified a compositematerial is obtained having a structure consisting of twointerpenetrating continuous spatial skeletons, the refractory carbidestructure and the metal, alloy or Si structure, offering a wide range ofproperties for various fields of application. Even at very highapplication temperatures, over the melting point of the metal, alloy orSi phase, the body retains its load-beaming properties. When thetemperature rises over the melting point of the metal, alloy or Si phasethe capillary forces keep the melt inside the article.

When the intention is to use the material/article as a catalyst, thewalls of the open pores in the semi-product are coated with a metallayer. The layer consists of at least one metal, or an alloy based on atleast one metal, from the group: Ag Cu, Ga, Ti, Ni, Fe and Co. Elementssuch as V, Cr, Pt, and Pd can be added to the alloy that is used coatingthe walls of the catalyst article.

Properties

As pointed out earlier in the text the semi-product obtained after thepyrocarbon process has the same shape and size as the porous bodyobtained in the molding process. Therefore not only composite materialbut also articles can be produced, the shape and dimension of such anarticle is determined by the shape and dimension of the blank. Thefinished composite materials manufactured by this method are hard andconsequently difficult to machine. But both the blank and thesemi-product manufactured by this method are possible to machine, whichmake the machining substantially easier. Thus at production ofcomplicated shaped articles it is advisable to do any machining beforeimpregnation.

An article made out of powder of at least one metal out of the group:Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W as outlined above has properties ashigh stability under intensive heat flows, self-lubrication at dryfriction, high damping ability, air arc resistance etc.

When TiC is used in the carbide skeleton structure and Ti, Al or Mg inthe impregnating melt properties as high specific strength and rigidity,low specific density, high strength at elevated temperatures, lowcoefficient of linear expansion, high electric and thermal conductivityand air arc resistance are received.

An article where the blank is made of a mixture of boron and/or silicon,and boron carbide and/or silicon carbide, and the impregnating melt isfrom the group: Si, Al, Mg, Cu or an alloy on the basis of one or moreof these element has properties as high specific strength and rigidity,high strength at elevated temperatures, low coefficient of linearexpansion, self-lubrication effect under conditions of dry friction andso on. Additional unique properties are low specific density when theimpregnating elements are Al, Mg, or Si. Additional properties when theimpregnating element is Cu are high electric and thermal conductivity,air arc resistance.

SUMMARY

The set of unique properties make it possible to use the compositematerials manufactured by the claimed method as refractory, structural,wear-resistant, erosion-resistant, tribotechnical (friction,antifriction), refractory damping materials as well as ablatingheat-protection materials, including those with low density and highspecific strength and rigidity.

Materials obtained by the claimed method retain high strength even athigh temperatures. At temperatures exceeding melting point of metalcomponent their strength corresponds to strength of carbide skeleton.The materials retain their shape in the range of high temperatures(unlike matrix composite materials which completely lose their shape attemperatures exceeding melting point of metal). After cooling thematerial recovers its structure and properties because the melt has beenretained in the carbide skeleton by capillary forces. Such a set ofproperties make application of these materials promising for movingparts of internal combustion engines, pumps, compressors, such aspistons and their components, components of cam drives, valves, valvefollowers, connecting rods etc. The articles can be used as componentsof parts or as inserts in the parts in places most subjected to wear ofvarious natures.

Articles of materials with aluminum, copper, alloys on the basis ofthese metals in pure state as metal phase can find application aselectrodes and contacts of electric equipment subjected to effect ofarc, components of friction couples, components of shaft face packingetc.

Very important advantages of the claimed invention are the following:

-   -   First of all, the use of carbides and metal and/or non-metal in        the powder makes it easier to achieve a favorable size        distribution of the powder particles in order to optimize the        packing properties of the powder. It provides the possibility to        optimize the composition and porosity of the blank even in case        of restricted choice of carbide and metal and/or non-metal        powders on the market.    -   Secondly the use of mixtures of carbide and metal/non-metal        carbide formers leads to a substantially decrease in the        duration of the pyrocarbon heat treatment in comparison with        prior art.    -   Thirdly in contrast to prior art, the use of both carbide and        carbide forming agent in the mixture makes it easier to keep the        porous body and semi product free of any distortion occurring        during the pyrocarbon- and activation-heat treatments, i.e. with        less effort put on controlling the process it is possible to        manufacture a high-quality article.

THE ESSENCE OF THE INVENTION IS DISCLOSED IN THE FOLLOWING EXAMPLESExample 1

Out of a mixture comprising 49% mass. of amorphous boron powder, 49%mass. of boron carbide powder with particle size 30 μm and 2% mass. of atemporary bonding agent (phenol formaldehyde resin SF 10-A) a blank isformed by pressing in the shape of parallelepiped, the dimensions being5×6×50 mm. The pores of the blank (porosity of 51% vol.) are uniformlydistributed through the volume. The blank is then placed in anisothermal reactor for pyrocarbon synthesis and is being heat-treated inan atmosphere of natural gas at 870° C. The increase of mass that willtake place during the heat treatment is calculated beforehand byequation (2) using the following values for the parameters:β=0.5; K=1.

The blank is treated in the reactor for 3.2 hours, until the in thisexample desired mass increase of 13.88%, has been reached. Then thesemi-product is placed into a vacuum furnace, being heated to 1650° C.and held at this temperature for 20 minutes. Furthermore, impregnationof the porous blank is carried out by dipping it into a melt of Al-12%Sialloy in the vacuum furnace at a temperature between 1150-1200° C. Afterthis an article is obtained with the same dimensions as those of theinitial blank. The article comprises 55% vol. of boron carbide and 45%vol. of the alloy (Al-12%/Si).

The material of the article possesses the following properties: Density(ρ)—2.56 g/cm³, hardness HRC—55, dynamic modulus of elasticity (E)—215GPa, flexural strength at 20° C.—402 MPa, at 200° C.—395 MPa, at 400°C.—225 MPa, at 500° C.—195 MPa, and at 600° C.—45 MPa Specific modulusof elasticity (E/9.81ρ)—8.46×10³ km.

One ought to pay attention to the very low density of the material andhigh specific rigidity, which are several times greater than theseparameters are in other materials. As well as to the temperaturedependence of the flexural strength which indicates a substantialexcellence of this material when compared to conventional low-densityalloys which cannot be used, as a rule, at temperatures above 400° C.

Example 2

Out of a mixture comprising 83.3% mass. of amorphous boron powder, 14.7%mass. of boron carbide powder with particle size 100 μm and 2% mass. oftemporary binder (a mixture of polyvinylpyrrolidone, polyethylene glycoland oleic acid) a blank is formed by pressing. The blank having theshape of a cylinder with the diameter 15 mm and the height 20 mm.Porosity of the blank is 65% vol. The obtained blank is heat treated inan atmosphere of natural gas at the temperature 850° C. until theincrease in mass reaches 23%. Then the se-product is placed into avacuum furnace, heated to 1650° C. and held at this temperature during20 min. Further, impregnation of the porous blank is carried out bymelting of a weight of alloy Al-12%/Si on the surface of the porousblank in the vacuum furnace at the temperature 1150-1200° C. After thisan article is obtained with the same dimensions as those of the initialblank. The article consists of 44% vol. boron carbide and 56% vol. alloy(Al-12%Si).

The article possesses the following properties: density —2.55 g/cm³,hardness HRC—40, heat conductivity at 20° C.—72 W/m.K, heat capacity at20° C.—950 J/kg.K, heat conductivity at 300° C.—53 W/m.K, heat capacityat 300° C.—1200 J/kg.K.

Example 3

Out of mixture consisting of 49.5% mass titanium-powder, 49.5%/masstitanium-carbide-powder and 1% mass temporary binder phenol formaldehyderesin SF 10-A) a blank is formed by pressing in the shape ofparallelepiped with dimensions 5×6×50 mm Porosity of the blank is 52%vol. uniformly distributed through the volume. The obtained blank isplaced into a isothermal reactor for pyrocarbon synthesis and heattreated in atmosphere of natural gas at the temperature 870° C. for 11hours until the increase of its mass reaches 12.5%. Then thesemi-product is placed into vacuum furnace, heated to 1580° C. and heldat this temperature during 20 min. Further, impregnation of the porousblank is carried out by dipping into melt of alloy Al-12%/Si in thevacuum furnace at the temperature 1150-1200° C. After this an article isobtained with the same dimensions as those of the initial blank. Thearticle consists of 48.5% vol. titanium carbide and 51.5% vol. alloy(Al-12%Si).

The article possesses the following properties: Density (ρ)—3.7 g/cm³,hardness HRC—31, dynamic modulus of elasticity (E)—196 GPa, flexuralstrength—435 MPa, specific modulus of elasticity (E/9.81ρ)—8.46×10³ km.

Example 4

Out of mixture consisting of 99%/mass. titanium powder and 1% mass.temporary binder (phenol formaldehyde resin SF 10-A) a blank is formed.Note this example is not included by the scope of this invention sinceit does not include the use of carbide in the powder that forms theblank. This example is used as one part in an illustration of the timegain that can be made when using carbide in the powder. A blank in theshape of a disc with the diameter 20 mm and the height 3 mm is formed bypressing. Then the blank is heat treated in atmosphere of natural gas atthe temperature 870° C. for 23 hours until the increase in mass reaches24.8%. Then the blank is placed into vacuum furnace, heated to 1580° C.and held at this temperature during 20 min. Further, impregnation iscarried out by melting of a weight of aluminum, Mark A7 (Al≧99.7%), onthe surface of the porous semi-product in the vacuum furnace at thetemperature 1200-1250° C. The article consists of. 50% vol.titanium-carbide and 50% vol. aluminum.

Material of the article possesses the following properties: Density(ρ)-3.79 g/cm³, hardness HRC-18.

Example 5

Out of a mixture of titanium (16 μm) and titanium carbide (10 μm) takenin mass proportion 1:1 and 1% mass. of temporary bond (phenolformaldehyde resin SF 10-A) a blank in the shape of parallelepiped withdimensions 5×5×50 mm is formed by pressing. Porosity of the blank is 50%vol. uniformly distributed through the volume. The obtained blank isplaced into an isothermal reactor for pyrocarbon synthesis and heattreated in an atmosphere of natural gas at the temperature 870° C. Theblank is held in the reactor for 10 hours until the increase in massreaches 12%. Then the semi-product obtained is placed into vacuumfurnace, heated to 1650° C. and held at this temperature during 15 min.Further, the obtained porous carbide skeleton is impregnated with anequiatomic alloy of nickel and titanium in the vacuum furnace at thetemperature 1300° C. by melting of a weight of the alloy on the surfaceof the blank during 5 minutes. The obtained composite material consistsof 51% vol. titanium carbide and 49% vol. nickel-titanium alloy.

The article possesses the following properties: density—5.5 g/cm³,hardness HRA—82, dynamic modulus of elasticity—230 GPa, a strength at3-point bending at 20° C. of—520 Mpa and the crack resistance K_(IC=)15Mpa. m^(1/2).

Properties of the material in al the experiments were determined by thefollowing methods:

-   -   1. Density was determined by hydrostatic method.    -   2. Hardness—by Rockwell method    -   3. Dynamic modulus of elasticity—by resonance frequency method    -   4. Flexural strength—by three-point bending method.    -   5. Crack resistance—by critical coefficient of stresses.    -   6. Heat conductivity and heat capacity—by monotonous heating        method.

1. A method of manufacturing a refractory carbide-based composite material, which comprises: molding a porous blank from a powder mixture of at least one carbide-forming metal and/or non-metal and at least one carbide; the amount of carbide component in the powder mixture not exceeding 90% by weight; heat treating the obtained porous blank in a hydrocarbonous atmosphere containing one or more hydrocarbons until the blank has increased 2-42% in mass, thereby obtaining a semi-product; and heating the obtained semi-product in a non-oxidizing medium at a temperature of 1000-2000° C. to obtain a heated semi-product.
 2. The method according to claim 1, further comprising impregnating the heated semi-product with a metal or alloy melt.
 3. The method according to claim 2, wherein the powder mixture comprises at least one carbide-forming agent selected from a first group consisting of: Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Si, B and at least one carbide out of said first group; the heat treatment of the obtained porous blank in a hydrocarbonous atmosphere is carried out until the mass increase reaches 2-25%; and the heated semi-product is impregnated with a melt of at least one element selected from a second group consisting of: Ag, Au, Cu, Ga, Ti, Ni, Fe, Co, Si or an alloy based on at least one element from said second group.
 4. The method according to claim 2, wherein the powder mixture contains titanium and titanium carbide; the heat treatment of the obtained porous blank is carried out until the mass increase reaches 7-25%; the heating of the obtained semi-product is carried out at a temperature of 1300-1600° C., and the heated semi-product is impregnated with a melt of at least one element selected from the group consisting of: Al, Mg, Si or alloy based on at least one element from said group.
 5. The method according to claim 4, wherein the powder mixture includes the following proportions of components in mass %: titanium 30-99  titanium carbide  1-70.


6. The method according to claim 4, wherein the powder mixture further includes a temporary binder and the following proportions of components in mass %: titanium 29-98 titanium carbide  1-69 temporary binder  1-5.


7. The method according to claim 2, wherein the powder mixture contains a mixture of boron and/or silicon and boron carbide and/or silicon carbide; the heat treatment of the obtained porous blank is carried out until the mass increase reaches 8-42%6; the obtained semi-product is heated at a temperature range of 1300-1800° C.; and the heated semi-product is impregnated with melt of at least one element selected from the group consisting of: Al, Mg, Cu, Si or alloy based on at least one element from said group.
 8. The method according to claim 7, wherein the powder mixture includes the following proportions of components in mass %: boron and/or silicon 30-99 boron carbide and/or silicon carbide   1-70.


9. The method according to claim 7, wherein the powder mixture further includes a temporary binder and the following proportions of components in mass %: boron and/or silicon 29-98 boron carbide and/or silicon carbide  1-69 temporary binder  1-5.


10. The method according to claim 6, wherein the temporary binder comprises phenolformaldehyde resin or a mixture of polyvinylpirrolydone, polyethylene glycol and oleic acid.
 11. The method according to claim 7, wherein the blank has a porosity of 30-70% by volume.
 12. The method according to claim 4, wherein the blank has a porosity of 30-60% by volume.
 13. The method according to claim 1, wherein the blank has a porosity of 20-60% by volume.
 14. The method according to claim 1, wherein the blank has a porosity, which is uniformly distributed through its volume.
 15. The method according to claim 1, wherein the blank has a porosity, which is non-uniformly distributed through its volume.
 16. The method according to claim 1, wherein the molding of the blank is carried out by pressing or slip casting or slurry casting.
 17. The method according to claim 1, wherein the heat treatment is carried out in an atmosphere of natural gas at a temperature of 750-950° C.
 18. The method according to claim 1, wherein the heat treatment is carried out in an atmosphere of at least one hydrocarbon selected from the group consisting of acetylene, methane, ethane, propane, pentane, hexane, benzene and derivatives thereof at a temperature of 550-1200° C.
 19. The method according to claim 2, wherein the impregnating is made either by dipping the heated semi-product into the melt of a metal, alloy or Si, or by melting an amount of a metal, alloy or Si on the surface of the heated semi-product.
 20. The method according to claim 19, wherein the heated semi-product is totally or partly saturated in the impregnating step.
 21. The method according to claim 2, wherein the walls of the pores in the heated semi-product are coated by a metal or an alloy in the impregnating step. 